814 BALANIDJB. 



I have not seen any form intermediate between them. It must, how- 

 ever, be confessed, that this is an extremely variable character in many 

 sessile cirripedes. In the Terga, the spur is about half the width of the 

 whole valve, and therefore rather wider than in A. spongites. 



5. ACASTA GLANS. PI. 9, fig. 5 a — 5 C. 



A casta glans. Lamar ck. Animaux sans Vertebres, 1818. 



Parietes internally quite smooth, with the lateral margins 

 of each compartment inwardly prominent : basis with the edge 

 rarely or enated, but furnished with six inwardly prominent 



teeth : scutum strongly striated longitudinally. 



Yar. (a) with the edge of the basal cup finely crenated. 



Hab. — New South Wales, Southern Australia ; Mus. Brit., Stutchbury, &c. 



This fine species seems to be extremely common, im- 

 bedded in an open porose sponge on the eastern and 

 southern shores of Australia. It is very distinct from the 

 other species, with the exception of the following A. Icevigata, 

 which, with some hesitation, I have allowed to remain spe- 

 cifically separated. 



General Appearance. — Excepting in its larger size, this species differs 

 in external appearance but little from A.spongites ; its colour is pale 

 dirty reddish. The surface is generally studded with small calcareous 

 points. The parietes of the carino-lateral compartments are about 

 one fourth of the width of the parietes of the lateral compartments, 

 and therefore proportionally of the same width as in A. cyathus. 

 The largest specimen which I have seen, was *55 of an inch in basal 

 diameter. 



Scuta.— These are slightly narrower, thicker, and more convex than 

 in A. spongites : they are strongly striated in longitudinal lines. The 

 articular ridge is very feebly developed. Terga : in full-grown speci- 

 mens, the spur is half the width of the whole valve, and is truncated ; 

 its basal edge being parallel to the basal margin of the valve. The 

 articular ridge and crests for the depressores muscles are very feebly 

 developed. 



Internal structure of the parietes. — The inner surface of the parietes 

 is quite smooth, without even a trace of ribs or teeth. But the most 

 important character is that the internal lateral margins on both sides of 

 each compartment, from the sheath to the basis, project inwards and 

 form a rim ; so that when the shell is viewed from within (PI. 9, 



